Photolithography is a technique for printing a pattern with features onto the surface of a substrate. A commonly-used substrate is a semiconductor wafer or a glass substrate having a surface coated with a light-sensitive material (e.g., photoresist). During a photolithography process, a wafer is placed on a wafer stage and the pattern is projected onto the surface of the wafer by means of an exposure device incorporated in the photolithography machine.
One of the important metrics for assessing the performance of a photolithography machine is exposure dosage, because the development of the photoresist will be affected at excessively high or low exposure doses. For this reason, exposure dose control accuracy poses a direct impact on the etching accuracy of the photolithography machine.
Exposure systems in existing medium-end and low-end photolithography machines employ high-pressure mercury lamps as their light sources. Such an exposure system utilizes a mechanical shutter disposed in the optical path to enable or disable exposure, and the exposure dose is determined by the exposure time.
Specifically, this operation may involve:
1) stabilizing an output optical power of the high-pressure mercury lamp by preheating or environmental control;
2) calculating the exposure time, opening the shutter to enable exposure and concurrently starting a timer; and
3) upon the expiration of the exposure time, closing the shutter to disable exposure.
In recent years, the output power of mercury lamps has been on a rise. This means that, at the same exposure dose, the time required for the opening and closing of the shutter must be shortened. However, due to the structural limitations of the conventional mechanical shutter, the shutter opening and closing time is already close to the limit, and increasing the power of the shutter simply increases the burden on the control system. Further, frequent overpowered operations may impair the stability of the system.
In order to overcome the above problem, there has been disclosed in the prior art a shutter device for use in an exposure sub-system of a photolithography machine, which can be quickly opened and closed under the action of high-power voice coil motors. However, in order to achieve a shorter shutter opening and closing time, the voice coil motors often have to operate at high power levels. Additionally, the voice coil motors themselves fail to meet the practical needs in terms of reliability and stability. As a result, many problems may arise from the operation of the shutter, which may ultimately affect the stability and performance of the photolithography tool in which the shutter device is employed.